Method of and means for bending tubes



Dee'. 2o, 1932. w, SNELL 1,891,338

IMETHOD OF AND MEANS FOR BENDING TUBES Filed Feb. 9, 1951 2 sheets-sheet1 CHR/VBE? Dec. zo, 1932. L, w. SNELL 1,891,338

METHOD 0F AND MEANS FOR BENDING TUBES Filed Feb. 9. 1931 2 Sheets-Sheet2 Patented Dec. 2G, 1932 LESTER W. SNELL, OF ALTON, ILLINOIS METHOD FAND `MEANS FOR BENDIN'G TUBES Application led February 9, 1931.` SerialNo. 514.848.

This invention relates to methods of and means for bending tubes, andthe novel features may be advantageously used in making pipe fittings,such as U-shaped return bends,

elbows with end portions at various angles to each other, and also inmaking long continuous coils of tubing.

One of the objects is to accurately bend the tubes to a'predeterminedcurvature, while preventing undesirable variations in the thickness ofthe tube walls. A further object is to produce a strong and simple benttube having a predetermined thickness which may be uniform throughoutthe tube.

In performing an ordinary simple bending o eration, a metal tube isstretched at the arc o greatest radius, which is termed the outerportion of the bend, while the metal is compressed at the inner portionof the bend,

0 where the radius of the curve is shorter. The

stretching in this old method reduces the thickness of the metal at theouter portion of the bend, while the compression increases the thicknessat the inner portion of the bend. As a consequence, the ordinary simplebending operation results in a bent tube. that is nonuniforln inthickness. l

In the preferred form of the present invention, the metal is of coursesubjected to varying changes in thickness during the bending operation,but these variations are so controlled that the bent tube is free fromobjectionable thick and thin portions. The tube is bent at hightemperatures, and I preferably subject it to different temperatures, soas to control the changes in thickness and at the same time preventobjectionable distortion of the tube.

An important object is to accomplish all of these results in a verysimple and inexpensive manner by merely pushing a continuous tubethrough a curved .passagewayv without using cores or the like inside ofthe tube.

The simple pushing operation imparts a longitudinal motion to the tubeand results in an upsetting action whichcauses a predetermined varyingchange in the thickness of the metal, thereby producing the desiredthickness in the finished tube.

I will hereafter show how this can be accomplished without decreasingthe thickness in any part of the tube during the lbending operation. Theupsetting operation causes` a varying increase in thickness around thecircumference of the tube, so the bending can be accomplished withoutundesirable stretching, or thinning, of the metal at the curve oflargest radius in the bend.

With the foregoing and other objects .in 6

view, the invention comprlses the novel method,"construction,combination and arrange` mentof parts hereinafter more specificallydescribed and illustrated in the accom anying drawings, wherein is shownthe pre erred embodiment of the invention. However, it is to beunderstood that the invention comprehends changes, Variations andmodifications which come within, claims hereunto appended.

Fig. 1 is a section illustrating a bending l system embodying thefeatures of this invention,

Fig. 2 is a section on the line 2 2 in Fig. 1,

Fig. 3 is a section on the line 3-3 in Fig. 1, 75

Fig. 4 is a transverse section on the line 4-4 in Fig. l, showingvariations in the thickness of the tube to be bent, and

Fig. 5 is a section on the line 5--5 in Fig.

1 showing the uniform thickness of the bent 80 tube.

I will now describe the apparatus which I have shown to illustrate oneform of the iiivention.

6 designates a forming die made of two sections contacting with eachother at the line 7 in Fig. 3, and alined by means of dowel pins 8, saiddie having a curved passageway 9 conforming to the curvature of the bent90 tube.

10 indicates a tube adapted to be forced through the passageway 9. Inthe preferred form of the invention, the first step consists in forminga continuous straighttube, of any o5 desired length, having thecross-section shown by Fig. 4. This long straight tube has a relativelythick portion which extends longitudinally of the tube, and thethickness gradually decreases circumferentially to a 100 the scope ofthe f p oint diametrically opposite said thick portion.

In other words, as shown in Fig. 4, the thickest portion of the tubetoibe bent lies directly opposite the thinnest portion, and there is agradual change in the thickness between these portions, the inner faceof the tube being eccentricto the outer face.

After this tube has been forced through the curved passageway 9, it iscurved as shown at the left of Fig. 1, and it has a uni-` form thicknessas shownin Fig. 5. This uniformity in thickness is due partly to theinitial non-uniformity in thickness, and partly to the upsettingoperation which occurs when the tube is subjected to the differenttemperature conditions hereinafter described.

11 desi ates a stationary guide tube (Fig. 1) exten lng from theentrance of the curved passageway 9 and conforming to the outer face ofthe straight portion of the tube 10. A heaiing chamber 12, surroundingthe guide tube 11, may be covered with insulation and provided withinlet and exhaust pipes 14 and 15 for the admission and discharge of theheating medium, which may be highly heated gases or other. suitableheating agent. The heat transmitted from this chamber 12 may be greatenough to subject the tube 10 to a uniform red heat while it passesthrough the guide tube 11.

The thickest portion of the tube 10 passes from the guide tube 11 to thecurve of largest radius invthe curved passageway 9, as shown in Fig. 1,while the thinnest portion of said tube 10 passes to the curve ofshortest radius in said curved passageway.

As an illustration of one means to produce the variations in thetemperature of the metal undergoing the bending operation, I have shownlocal coolers 16 and local heaters 17 at the entrance to the curvedpassageway, and a local heater 18 in the form of a burner projecting aflame onto the portion of the die 6 at points adjacent to thebending-zone of the relatively thin portion of the tubelO. However, it1s to be understood that the invention is not limited to these details.

The local coolers 16 lie at the thickest and thinnest portions of thetube to be bent, while the `local heaters 17 are in the form of burnerswhich project ames onto the guide tube 11 at points between said localcoolers 16. As shown b Fig. 2, the local coolers 16 may be provide withinlet and discharge pipes 19 and 20 through which a cooling fluid istransmitted.

The tube 10 is pushed through the guide 11 by any suitable power, an isgradually heated to a uniform high temperature by the heat transmittedfrom the surrounding cham# ber 12.

However, instead of merely bending a simple hot tube, I preferablyperform a complex upsetting actionwhich thickens all parts of the tube,excepting the thickest portion in Fig. 4, and I preferably prevent anysubstantial stretching, or thinning, of said thickest portion. In otherwords, instead of performing a simple bending operation which stretchesand thins the metal at the curves of relatively large radius in thebend, while compressing and thickeninfr the metal at the curves ofshorter radius, fpreferably com-l pact and thicken the metal at allpoints where there is any change in thickness. The bending can thus beperformed by thickening all of the metal to the maximum thickness shownin Fig. 4, without reducing the thickness any point.

The heat from the annular heating chamber 12 preheats the entire tube 10rto about a light red heat, and the preheated tube then passes the localcoolers 16 and the local heaters 17 at the entrance of the curvedpassageway.

The relatively thick portions of the tube are thus cooled by one of thelocal coolers 16 and placed in a relatively firm condition. Thisprevents undue changes in the thickness of said thick portions, and alsoprevents undesirable displacement or distortion of said portions. At thesame time, the other local cooler 16 reduces the temperature of the thinportions of the tube as they enter the curved passageway 9. The thinportions are thus stifl'ened to prevent crimping, or folding, of thethin metal near the entrance of theI curved passageway. The action atthis point may not be apparent, but one should understand that lthelongitudinal pressure on the tube 10 tends to force the thin portionsaway from the wall of the curved passageway, and that there is atendency for these thin portions to fold, or buckle, at the beginning oftheir I bending action. However,- as the thin portions approach thecurved bending zone 1n a relatively cool and firm condition, and sincethey are also reinforced by the firmer thick portions, the thin metal isnot subjected to an undesirable displacement at the entrance of thecurved passageway 9.

However, to provide for the intense upsetting and thickening of said-thin metal, it is rapldly heated. bythe burner 18 which results in thedesijfefdi'imion of this metal, and prevents foldingfor crimping of thethin metal as its particles are united to thicken the tube. Astrong'tube structure, free from laps or other defects yis, therefore,produced at the arcs of relatively short-radius in the bend.

The local heaters 17 transmit heat to oppo site 'sides of the tubeatjpoints between the thickest and thinnest portions of the metal. Themetal of the intermediate thickness is thus increased in temperature topermit the The temperature lof the thinnest portions of the tube ispreferably higher than that .of the intermediate ortions, as theupsetting and thickening' of) the thinnest portions is most intense. Alocal cooler 2l may therefore be located in the bending die, as showninFig. 1, to rapidly cool the highly heated upset metal passlng from thezone of the local heater 18. This highly heated metal, after being bentand thickened is accordingly 10 placed in a relatively firm condition,so it I passageway 9. However, the same longitudiwill not be pushed awayvfrom the wall of passageway 9, nor otherwise distorted.

Attention is now directed to' some of the peculiar actions which occurduring the bending operation.

The -longitudinal motion imparted to the straight portion of the tubevery. firmly pushes the thickest portion of the tube onto the curve oflargest radius in the curved nal motion tends to push thediametricallyopposite thin portion of the tube away from the oppositewall of said curved passageway. Nevertheless, the thick and relativelycool portion of the tube is positively pushed onto said curve of largestradius, and it is, therefore, positively bent to the desired curvature.This bending of the relatively cool and firm thick portion results inthe transmission of compressive strains tol all of the thinner metal.The -displacement ofthe metal under this compression gradually increasesfrom a minimum at the thick portion to a maximum at the thinnestportion. The temperature 5 and firmness of the metal likewise increasesfrom said thickest portion to said thinnest portion.

As a consequence, there is a varying upsettin and thickening action, theintensity of 40 which gradually increases from the thick portion of thetube to the thinnest portion. The

energy required for this upsetting opera-tion is transmitted from thethick portion of the tube to the thinnest portion, and it will beimportant to observe that all of the varying 5 to transmit the requireddegree of compression to the still hotter and thinner portions, @1erethe greatest increase in thickness oc- ,curs y i In this connection 1tmay also be noted that c3 while the longitudinal thrust imparted to thestraight portion of the tube has a tendency to push the thin portionsaway from the wall of the curved passageway 9, this tendency is firmlyopposed b the transmission of the 'bendmg thrust rom the relatively firmible thinner portions.

The thinner portions are, therefore, firmly forced onto the wall of thecurved passageway, where they are positively upset and thickened whileunder a pressure which causes the entire outer face of the tube toconform precisely to the curved face of said wall. The. finished tubehas a smooth outer face of a predetermined diameter, and the peculiarcombination of conditions prevents the formation of folds and otherirregularities during the highly complex bending and upsettingoperation.

It will now be vunderstood that a tube having the non-uniformcross-section shown in Fig. 4 is bent while subjected to a. -non-uniformtemperature which ishighest at the thin portion of the tube, anddecreases circumfer- -entially to the relatively low temperature at-thicker portions to the hotter and more fiexthe thickest portion of thetube.- This method produces a strong tube structure, free from thedefects which ordinarily occur in bending a-tube, and while. theinvention can be employed to produce bent tubes of varying thicknesses,one of the advantages lies in producing a bent tube, as shown in Fig. 5,hav- I ing a uniform thickness corresponding to the thickest portion ofthe tube shown in Fig. 4.

Moreover, the method can be very easily and quickly performed bymaintaining the desired temperature conditions, while the tube is merelypushed through the curved passageway 9.

A further advantage lies in the continuousoperation which permits a longcontinuous tube to be converted into a continuous bend, or coil, whichmay be used as a coil or cut into sections to produce elbows, returnbends l and the like. v. The: continuous bending operation can becarried out for an indefinite period-upon a.

continuous succession of straight tubes, ar-

ranged end to end, so that an incoming tubev willpush the preceding tubethrough the tubular guide 11 and thence through the curved passageway 9.

This simplecontinuous operation eliminates the necessity of usingremovable cores inside of the bending die, and it provides the A desiredaccuracy in the shape and thickness of the bent tube. Thepositivebending without distortion, and the freedom from weakening defects, arealso important.

While the variations in temperaturel at the bending zone may be obtainedby using any suitable heatin or heating and cooling, devices, itis usuay important to push the tube at a uniform speed, so as to .avoid undueincrease or decrease in the predetermined temperatures resulting fromthe transmission of heat to the moving tube.

It is also advisable to form a slight taper in the passageway 9. Forexample, to producea tube having an external diameter ofl 2% inches, thecurved passageway may have a diameter of 2", inches at the entrance,tapering to 2% at a radial line where the combined bending and upsettingoperation is completed.

In my copending application for patent on Methods of and Means forBending Tubes, Serial No. 440,254, iiled March 31, 1930, I have shownand more broadly claimed the method of bending tubes while forcing themthrough a curved passageway.

Iclaim:

1. The method of bending a tube having thick and thin portions whichcomprises imparting a longitudinal upsetting thrust to the thick andthin material undergoing'the bending operation, maintaining said thmmaterial at a relatively high temperature topermit free upsetting andthickening thereof, and maintaining said thick material at a lowertemperature, so as to produce a bentv tube havlng a substantiallyuniform thickness. v

2. The method which comprises bending a tube having a varying thicknessdecreasing circumferentlally from a relatively thick portion to athinner portion diametrically opposite said thick portion, imparting alongltudinal upsetting thrust to the material unergoing the bendingoperation, heating the tube and controlling the upsetting action at therelatively thin portions by subjecting said thin portions to-temperatures higher than that of the thicker` portions, so as toproduce the desired increase .in the thickness of said thin portions.

3. The method which comprises bending a tube having a varying thicknessdecreasing circumfeiitially from a relatively thick portion tq"`," Ainner portion diametrically opposite said`thick portion, imparting alongitudinal upsetting lthrust to the material undergoing the bendingoperation, subjecting the thin-portions to relatively hi h temperaturesto permit free upsetting an thickening Hof said thin portions during thebending operation, while subjecting the thicker portions toA lowertemperatures to prevent unda thinkening thereof.

4. The method of bending tubes which comprises forcing a tube through acurved passageway by pushing the outer face of the tube onto the wall ofsaid passageway, so as to bend and at the same time change the thicknessof the material forming different portions of the tube, heating the tubeand producing different temperatures in different portions of thematerial undergoing the bending operation, so as to control thevariations in thickness resulting from the heat and pressurento whichthe tube is subjected in said curved passageway. v

5. The method 'of bending tubes whichcomprises forcing a continuous tubethrough a curved passageway by pushing the outer face of the tube ontothe wall of said passageway, so as to bend and at the same time changeent portions of the tube, heating the tube and the thickness of thematerial forming diifer- L producing different temperatures in differenttions in thickness resulting from the heat A and pressure to which thetube is subjected in said curved passageway, and maintaining anapproximately uniform speed in the longitudinal movement o f thecontinuous tube so as toprevent substantial variations in thepredetermined temperatures at different portions of the moving tube.

6. The method of bending atube having thick and thin portions, whichcomprises forcing the tube through a curved passageway'by pushing theouter face ofthe tube onto the wall of said passageway, so as to bendand at the same time change the thick' ness of the material formingdifferent portions of the tube, heating the tube and producingrelatively high temperatures in the -thin portions of the materialundergoing the bending operation. so as to permit relatively freeupsetting and thickening of said thin portions in response'to the heatand pressure to'which the tube is subjected in said curved passageway,and at the same time maintaining lower temperatures in the thickportions undergoing the' bending operation so as to prevent excessivechange in the thickness of said thick portions.

7 The methodof bending a tube having thick and thin portions, whichcomprises forcing the tube through a curved passageway -by pushingtheouter face of the tube onto the wall of said passageway, so as to bendand at the same time change the thickness of the material formingdifferent portions of the tube,'heating the tube and producingrelatively high temperatures in the thin portions of the materialundergoing the bending operation, so as to permit relatively.

free upsetting -an-d thickening of said thin portions in response to theheat and pressure to which the tube is subjected in said'curvedpassageway, at the same time maintaining lower temperatures in the thickportions undergoing the bending operation so as to prevent excessivechange in the thickness of said thick portions, and maintaining anapproximately continuous uniform speed in the longitudinal motion ofsaid tube, so as to provide for the transmission of the differentpredetermined degrees of heat to different portionsof the moving tube. y

8. The method which comprises forming a tube having a' varying thicknessdecreaslng circumferentially from a relatively thick portion to a thinportion diametrically opposite said thin portion, Aforcing said tubethrough a curved passageway by pushing the outer face of the tube ontothe wall o'f said passageway, so as to bendand at the same time changethe thickness of the material forming different portions of the tube,heating the tube and producing` di'erent temperatures in differentportions of the material undergoing the bending operation, the highesttemperature being in the thin portion of the tube to permit freeupsetting and thickening of said thin portion in response to the heatand pressure in said curved passageway, the thick portions of said tubebeing maintained ata lower temperature in they bending zone to check theupsetting action in said thick portions. f

9. The method which comprises forming a tube having a varying thickness`decreasing circumferentially from a relatively thick portion to a thinportion diametrically opposite said thin portion, forcing said tube at asubstantially uniform. speed through a curved passageway by pushing ythe outer face 'of the tube onto the wall of said passageway, so as tobend and at the same time change the thickness of the material formingdiiierent portions of the tube, transmitting heat to said tube while itis moving at said uniform speed and producing different temperatures indifferent portions of the material undergoing the bending operation, thehighest temperature being in the thin portion of the tube to permit freeupsetting and thickening of said thin portion inresponse to the heat andpressure in said curved passageway, the thick portions of said tubebeing maintained at a lower temperature in the bending zone to check theupsetting action in said thick p-ortions.

10. The method of producing curved tubes which comprises forming a tubewith a relatively thick portion longitudinally of the tube, the'thickness decreasingl circumferen-` tiallyto a point diametricallyopposite said thick portion, heating and then bending said tube `byupsetting the relatively thin portions while maintaining said thinportions at a temperature higher than that of the relatively thickportions, so as to permit relatively free upsetting and thickening ofsaid relatively thin portions.

11. The method of producing curved tubes which comprises forming astraight tube with a relatively thick portion arranged longitudinally ofthe tube, the thickness decreasing circumferentially to a pointdiametrically opposite said -thick portion, imparting acontinuous,`uniform longitudinal motion to the straight portion of saidtube while. heating and then gradually bending said moving tube byupsetting'. the;` relatively thin Iportions while maintaining said thinportiqpsfat a temperature higher than that of thei'elativevly thickportions, so as to permit relatively free upsetting and thickening ofsaid relatively thin portions.

12. The method of producing curved tubes which comprises forming a tubewith-a relatively thick Iportion arran ed longitudinally of the tube,the thickness ecreasing circuml. .is

erentially to a point diametrically opposite.

said thick portion, heatingand then bending said tube by locating thethickest portion at the curve of largest radius in the bend whilemaintaining the varying thinner portions, at relatively high temeratures, so as to freely upset and thicken said thinner portions with-I out materially changing the thickness of said thickest portion.

13. The method of producing curved tubes substantiall uniform inthickness, vwhich compriseso'rming astraight tube with a relativelythick portion arran ed longitudinally of the tube, the thicknessdecreasing circumferentially to a point diametrically opposite'saidthick portion, heating and then bending said straight tube b locatingthe thickest portion at the curve o largest radius in the bend andupsetting the varying thin- 'ner portions to the thickness of saidthickest portion.

'14. The method of producing curved tubes substantiall uniform inthickness, which comprises fbrming a straight tube with a relativelythick portion arranged longitudinally of the tube, the thicknessdecreasing circumferentially to a point diametrically opposite saidthick ortion, heatin and then bending said straig t tube by pushlng itlongitudinally at a uniform speed through a curved passageway with thethickest portion of the tube in contact with the curve of largest radiusin said passageway, at the same time transmitting heat to the movingtube and maintaining the relatively thin portions at relatively v'nightemperatures, so as to upset all of said thin portions to a thicknesscorresponding approximately 'to the thickest and then rapidly coolingsaid portion to prevent distortionthereof.

16. The method which comprises moving a tube lon itudinally at asubstantially uniform spee at the same time bending the tube andtransmitting varying degrees of heat to different portions of said tube,so as to control the changes in thickness during the bending operation,providing the highest temperature in the portion at the curve of shortest radius in the-bend to permit free upsetting and thickening of saidportion durin the bending operation, and then rapidly coo ing saidportion.

17. In a tube bendlng apparatus, a bending die having a curvedpassageway through which the tube is forced to form the desired bend,and means whereby different portions of the tube are subjected todiiferent temperatures durin the bending operation, said means inclu inga heater to increase the temv rature of the-tube as it passes to thebend- A lng die, and a local cooler. ad'acent to the 'course of thetube, 'so as to uce the teml 'perature in a local area extendinglongitudinally of the tube.

18. In a tube bending apparatus, a bend'- ingdie having a curvedpassagewa through "1o which the tube isfomed u, form t e desired bend,and means'whereby diferent portions of the tube are subjected todiferent temperatures d the bending operation, said means inclu ing amain heater whereby the tube is heated as-it moves toward the bendingdie, local heaters at opposite sides ofthe tube to increase thetemperature at said opposite v sides, local coolers to reduce thetemperature between said vopposite sides, and a local heater adjacent tothe curve of shortest radius in said curved p wa y. In( testimony thatclaim the foregoing I hereunto aiiix my srature.

. STER W. SNELL.

